1. Technical Field
The present invention relates to a sheet conveying device which is excellent for application to image forming devices which, while successively conveying sheet-shaped recording media at uniform intervals, carry out processings for forming images onto the respective sheets.
2. Description of the Related Art
Generally, there are image forming devices and image reading devices which are provided with sheet conveying devices. The sheet conveying device is for conveying sheet-shaped image recording media, which are stocked in a supplying section, to a processing section which carries out various processings such as image forming processing, reading processing, or printing processing.
For example, among sheet conveying devices used in image reading devices such as copiers, fax machines, image scanners and the like, there are sheet conveying devices which separate, one-by-one, sheet documents which are stacked in a sheet supply tray, and automatically convey and supply the sheet documents to an image reading section.
In such a sheet conveying device, when the speed at which the sheet documents are supplied and the document reading speed in the image reading section are different, the interval between the sheet documents is no longer maintained at an appropriate uniform interval in the image reading section. Namely, if the document reading speed in the image reading section is fast, the interval between the sheet documents becomes long, and there is the concern that the time over which the sheet documents are processed will become long. Conversely, if the document reading speed in the image reading section is slow, the interval between the sheet documents becomes short, and there is the concern that a subsequent sheet document will collide with a preceding sheet document such that abnormalities in conveying will arise.
Therefore, conventional sheet conveying devices are provided with: sheet supplying means for supplying sheet documents toward a predetermined position; conveying means for continuously causing a preceding sheet document and a subsequent sheet document supplied from the sheet supplying means to pass through the predetermined position; setting means for computing and setting an interval between the preceding sheet document fed by the conveying means and the subsequent sheet document fed by the sheet supplying means, from a feed amount of the preceding sheet document and a feed amount of the subsequent sheet document within a predetermined period of time; and supplied sheet driving means for controlling driving of the time of the start of operation of the sheet supplying means, on the basis of the interval set by the setting means, wherein the intervals between the sheet documents successively passing through the predetermined position is reliably held constant, and the speed for processing the sheet documents is shortened (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 2002-179266).
In such a sheet conveying device used in an image forming device or an image reading device, when an attempt is made to effect control such that the sheet documents are conveyed at a faster speed, it is difficult to, on the basis of the feed amount of the preceding sheet document and the feed amount of the subsequent sheet document within the predetermined time period computed at the setting means, effect control such that the preceding sheet document and the subsequent sheet document do not contact one another. Moreover, if the sheet conveying device is structured so as to carry out switching-back on the conveying path of the sheet documents, it is difficult for the setting means to compute the feed amount of the preceding sheet document and the feed amount of the subsequent sheet document within the predetermined time period. In addition, when the sizes (the conveying direction lengths) of the sheet documents change, it is difficult to effect control such that the interval between the preceding sheet document and the subsequent sheet document is uniform.